Large amounts of gas hydrates exist on continental slopes, and pose a significant risk of triggering submarine landslides, subsequently impacting offshore infrastructures. While the infinite slope model is widely used for submarine slope stability analysis, it overlooks the potential for initial small failures to develop into large landslides. Our study integrates slip nucleation with excess pore pressure during gas hydrate dissociation, establishing a model for progressive slope failure triggered by hydrate dissociation. Focusing on the Shenhu hydrate site GMGS3-W19, our results show that even 1% gas hydrate dissociation contributing to about 1 MPa overpressure can induce progressive landslides. Notably, deeper failure surfaces with gentler slopes and collapsible sediments require higher pore pressures to induce progressive failure, reducing the risk of developing into catastrophic landslides. The results indicate that the infinite slope model may overestimate slope stability, and that submarine landslides caused by progressive failure may occur on slopes previously considered stable, such as the Ursa Basin in the northern Gulf of Mexico. This extension of the infinite slope model sheds light on potential limitations in current stability assessments, providing crucial insights for submarine landslide studies and offshore infrastructure development.